Questions tagged [fft]

FFT is an acronym for Fast Fourier Transform. Use this tag for FFT-related questions. Try to also select a specific chip or software tag when possible.

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17 views

Arduino FFT noobie question [migrated]

How do you obtain the real and imaginary parts of a signal using FFT in arduino? I could not find a particular tutorial with code for this purpose in the internet.
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4answers
138 views

FFT of a square wave

I'm generating a square wave as PWM whose frequency is set to 25 Hz. On the oscilloscope, I've got: The data referred to the image above was stored and maniputed, then I plot it using jupyter ...
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1answer
34 views

Quantization results in harmonics in ADC FFT plot

This is taken from Analog-to-Digital Conversion by Marcel Pelgrom. Okay, I understand that with 1-bit quantization, the output is block-wave (Square) and that of course when you do the Fourier Series,...
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1answer
58 views

FFT in oscilloscope measuring Frequency spectrum

I am using a Keysight InfiniiVision MSOX3054T Scope having Bandwidth of 500MHz and Sampling rate of 5Gsa/s. I am learning to use the FFT Option in the scope. Below is the waveform I captured of my ...
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1answer
38 views

Fourierspectrum of the output voltage of an real inverting amplifier

First a quick descripton of my circuit: The inverting amplifier amplifies by 20dB, the input voltage is a sinus signal with the Frequency 10 kHz and the peak to peak voltage is 200mV or 10V. The used ...
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19 views

How do I calculate individual output power from overall power from a wind farm through harmonic analysis?

Lets take my problem from the beginning: I take some measurements from a specific wind farm 10.8MW of local area in my country with a power quality analyzer for a certain time, with 256 samples N, 0....
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46 views

Estimating FFT error

I'm interested in trying to estimate the worst-case error when using a particular DFT implementation (CMSIS) and an ADC and voltage reference with known error bounds. I think that I can work out the ...
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1answer
83 views

Using an FFT to identify noise

First off, please note that I am a hobbyist. I have a couple of line level audio outputs that are picking up noise from a nearby 12v signal anytime it pulses. These pulses are translating into ...
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51 views

Sampling Frequency of a pulsed radar signal

I'm new to radar. please excuse my question if it doesn't make sense to you. In a pulsed radar signal, why is the required sampling frequency "2 times the inverse of pulse width" instead of "2 times ...
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2answers
78 views

How to interpret the FFT of the mains voltage in this case?

I coupled the 230Vrms AC mains voltage to a scope channel through a 10Vpk-pk step-down transformer. I can imagine the transformer will already filter high freq. noise but I thought I can still see ...
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2answers
76 views

PSD vs FFT of voltage magnitude squared and oscilloscopes

Imagine we have a time-domain signal which is a voltage signal. Now if we sample this at the correct rate, and taking the Fourier transform gives us the magnitudes of various frequency components ...
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2answers
108 views

Guitar to MIDI conversion

I am wanting to measure the pitch of a single guitar string and convert into MIDI within 10ms. FFT takes too much time, I was wondering what other options are worth looking at? The main issue is ...
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63 views

Monitoring 32 photodiodes simultaneously (all mounted on a flat surface)

I'm a total newbie here. I do not know much about circuits. So sorry for the newbie question and Thanks for helping! What I want to do is to detect position of incident light on this surface. For ...
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1answer
55 views

How to see Signal frequency and Sampling frequency on the frequency spectrum

If I have a 100 Hz periodic analog signal and let us say it is band limited to 1kHz and I sample it at 3 kHz. If I want to see its frequency spectrum then how to differentiate between the signal ...
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2answers
80 views

Can we use both FFT and PSD to obtain a random signal's frequency domain representation?

I always encounter random noise frequency domain representation as PSD(not FFT), something like in the below plot: Without diving into math too much, practically speaking can we always use FFT ...
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51 views

DIY high fidelity audio using delta sigma adc

This question may be too general, but I will include all the details that I can. My end goal is to achieve a super high-resolution spectrogram of any recording I choose to make. By doing some tests I ...
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1answer
67 views

Decoding Signals from an Unknown Port on Spectrometer

We have a Thermo-Nicolet Nexus 670 FT-IR Spectrophotometer, made in the USA around 2000. It was the work horse of the infrared spectroscopy community. The instrument sends out signals to a proprietary ...
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1answer
54 views

headphone input to arduino for FFT usage

I am building a FFT audio-reactive project with an Arduino that I would like to add a line-in input to. I am most likely to be using a ATTiny84 or ATTiny85 as the sampling device, which is running at ...
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2answers
154 views

How to find the source of a noise in a particular band

The problem: The ADSL2+ service at home is not performing up to its potential. The modem is supposed to sync at 16 Mbps (downstream) but the it does only up to 11.5 Mbps. Using the diagnostic tools ...
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36 views

Transfer Function Estimate and PSD

I am looking at using Matlab to estimate the transfer function of an unknown system using input and output time history data. I found this page: https://www.mathworks.com/help/dsp/ug/estimate-the-...
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2answers
78 views

Frequency Response Function Estimate via FFT Question

I want to estimate the FRF of a dynamic LTI system given experimental input and output data. I know generally the approach is to use a chirp as an input to make sure enough frequency content is ...
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2answers
122 views

dsPIC33E ADC to FFT help

I am sampling an audio range signal with a bandwidth of 3100Hz and then applying a FFT using the DSP library example from Microchip to determine the most dominant frequency of the signal. On the last ...
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0answers
322 views

In LTspice can I convert the units of an FFT which by default seem to be shown in dBV to dBµV?

In LTspice can I convert the units of an FFT which by default seem to be shown in dBV to dBµV? Cause of reason: The reason for this is that I've a modeled a LISN in LTspice where I want to simulate ...
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1answer
144 views

Can the transient response of a system be calculated using FFT and inverse FFT?

I have a system, its input and output has the following relationship. I want to know the transient response of the system with respect to a ramping input Xi=t, by solving the differential equation, ...
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49 views

What could be the source of this noise?

Below is the output of an accelerometer when it is standing still: The zoomed 0.5 seconds of time series voltage data above is from a 4 seconds of measurement with a data acquisition board at 30kHz ...
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3answers
87 views

Why is the dB of the FFT plots exceeding 96dB for these signals sampled by an 16 bit ADC

There is a 16-bit data acquisition board and below is the recording of 120 seconds of voltage input at 500Hz sampling rate. The blue plot corresponds to the input voltage Vin and the green plot output ...
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1answer
68 views

How to change FFT spike to curve

The first picture is a part of my circuit and the voltage pass through the high filter circuit. The second picture shows an FFT spike which is obtained from the .csv file created by oscilloscope. I ...
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0answers
30 views

non-negative FFT spectrum, subtlety

definations \$x(t)\$ is a function of time. Physically, it can be voltage, displacement, magnetization and so on. It can be real, complex, vectors or more fancy numbers. \$C(t)\$ is the auto ...
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565 views

Interpretation of FFT FMCW Doppler radar results

After a lot of research and help from the users here, I managed to do some FFT and signal processing in my first time in my life :) I have got the following figure, which shows one peak frequency, ...
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0answers
149 views

Getting the velocity in Radar FMCW

I have managed to get the frequency (the beat) frequency from an FMCW. Here is a screen shot of a wall that's detected by the Radar. I performed an FFT of complex I,Q data. My questions are 1. How ...
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1answer
837 views

Applying FFT on I/Q signal to get range and velocity

I managed to get correct I/Q signal from an FMCW radar. From my last questions I understand that I have to do FFT on the root of I^2+Q^2 so I will have an array of I^2+Q^2 then do FFT on it. My ...
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1answer
143 views

Signal processing of an IVQ-3005 Radar Module

I'm going to use that module for detecting range, velocity and angle, for that radar. https://www.innosent.de/fileadmin/media/dokumente/datasheets/180222_Datenblatt_IVQ-3005.pdf So I have read a lot ...
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2answers
119 views

A sensor which can measure the vibration of a material

I am planning on making a musical instrument where I require the conversion of vibration of a material to voltage. The idea is to make a percussion instrument where I hit a plate made of a certain ...
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3answers
134 views

Help interpreting strange spectrum

I am sampling a sinusoidal signal with an oscilloscope and viewing its spectrum using the FFT mode. The signal in time domain is this: and I am getting this spectrum: The peak above the red line is ...
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0answers
435 views

Wrong FFT result when using rfft function on STM32F4

I'm trying to use rfft function in STM32F407G and I am getting wrong results when I compare it with an online fft calculator . I give a sample input as {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,...
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3answers
2k views

What's the junk at the end of my FFT in LTSPICE?

Why do FFTs have junk on the high frequency end? Suppose I go to simulate this circuit in LTSPICE: simulate this circuit – Schematic created using CircuitLab Where the LTSPICE sine and ...
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1answer
484 views

Getting different FFT results in LTspice comparing to MATLAB and Python

I have a 10 seconds of sampled data. Sampling rate is 1kHz. I uploaded the text file which is a two column time vs voltage data; it can be downloaded here. I performed FFT in MATLAB, Python and ...
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2answers
2k views

How to choose a cut-off frequency by interpreting FFT

I have a question concerning low pass filtering of IMU acceleration and gyro data. To choose a reasonable cut-off frequency, I thought about making some observations in the spectrum. Now I have some ...
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6answers
3k views

Audio spectrum analysis: PC Software vs Hardware Spectrum Analyzer

I need to do some audio spectrum analysis (basically, listening to a machine and tell if it is properly calibrated). I will record the sound it makes with a microphone (it sounds differently if it is ...
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1answer
79 views

AM radio Attenuation.

I have built the following AM radio circuit : I was able to pick several radio stations. I fixed the variable capacitor so that I can only hear the 1230 kHz station which I identified from the FCC ...
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1answer
30 views

A signal noise analysis method question for a transducer

Let's say a transducer's desired signal is p(t), and the transducer's frequency of interest is 100Hz. And let's assume we dont know the total signal x(t) which is the desired signal plus the noise and ...
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1answer
44 views

Why averaging in Spectral magnitude domain not in complex domain to estimate spectrum of a process

Consider we need the magnitude spectrum of the signal. Signal is recorded in \$N\$ trials to a certain stimuli. Signal varies from each trial because of noise. So, to estimate the actual magnitude ...
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1answer
101 views

How to scale output of butterfly unit radix 2 for further stages?

I am designing 8 point FFT by radix 2 using verilog. I am using radix 2 butterfly unit with 8 bits input and so output. I expect to be 8 bit so that I can use this structure again and again for ...
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1answer
63 views

FPGA Frequency Domain Based Beidou-3 B2a Coarse Acquisition Processor Using FFT

I'm using an ARM+FPGA platform to capture B2a (BeiDou or COMPASS) signals and determine the user position, velocity and precise time (PVT). The C/A frequency of B2a is 10.23MHz. If my sample rate is ...
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1answer
112 views

fast Fourier Transform difference with discrete Fourier Transform

I'm a french student in engineering and I'm given a kind of mandatory technical project to work out on until February. I must investigate the following article: Precise and fast spatial-frequency ...
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6answers
7k views

Why use the fast Fourier transform for noise reduction instead of a classical electronic filter?

I'd like to know how to remove environmental noise from a speech recording. I've made some research and I've noticed that most of the methods proposed use the fast Fourier transform. But why can't ...
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0answers
631 views

RFFT on 8192 samples in Q15 with CMSIS

I need to perform an FFT on a block of 8192 samples on an STM32F446 microcontroller. For that I wanted to use the CMSIS DSP library as it's available easily and optimised for the STM32F4. My 8192 ...
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1answer
45 views

Linear Frequency Dependent IQ Distortion

I want to design FD (frequency dependent ) IQ (In-phase,Quadrature) distortion that changes the phase mismatch linearly like a+b*K ( where K is 1 to 64) and amplitude remains constant to test my ...
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2answers
400 views

Gain factor in real Resistance and Reactance (AD5933)

I'm trying to develop a system for bioimpedance measurement with the IC AD5933. The AD5933 is a high precision impedance converter system that combines a frequency generator with a 12-bit, 1 MSPS, ...
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1answer
229 views

Why do I get a high peak in my FFT plot of a 50 Hz sine wave?

I am plotting the FFT of my signal that is stored in "Array" format obtained from simulation. The signal is a sine wave of 50 Hz so I get a peak at 50 Hz. The problem is that the value is way too high....